////////////////////////////////////////////////////////////////////////////////
// This file is part of the Mist compiler.                                    //
//                                                                            //
// Copyright (C) 2008, 2009 The Mist project                                  //
//                                                                            //
// For a list of contributors, see the COMMITTERS file.                       //
//                                                                            //
// The Mist compiler is free software: you can redistribute it and/or modify  //
// it under the terms of the GNU General Public License as published by       //
// the Free Software Foundation, either version 3 of the License, or          //
// (at your option) any later version.                                        //
//                                                                            //
// The Mist compiler is distributed in the hope that it will be useful,       //
// but WITHOUT ANY WARRANTY; without even the implied warranty of             //
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the              //
// GNU General Public License for more details.                               //
//                                                                            //
// You should have received a copy of the GNU General Public License          //
// in the COPYING file. If not, see <http://www.gnu.org/licenses/>.           //
////////////////////////////////////////////////////////////////////////////////

///
/// \file
/// Contains the necessary declarations to make a class a singleton class.
/// A singleton class enforces that it has not more than one instance and
/// provides a centralized way of accessing that instance.
///

#ifndef SINGLETON_HPP
#define SINGLETON_HPP

////////////////////////////////////////////////////////////////////////////////
// Includes                                                                   //
////////////////////////////////////////////////////////////////////////////////

#include <boost/scoped_ptr.hpp>
using boost::scoped_ptr;

////////////////////////////////////////////////////////////////////////////////
// Singleton Class                                                            //
////////////////////////////////////////////////////////////////////////////////

/// A class that implements the basic functionality of a singleton class.
/// To make another class (T) a singleton class, make Singleton<T> a friend of
/// class T, then make the T constructor private or protected.
///
template <class T>
class Singleton {
	public:
		
		/// \return the sole instance of type \a T
		///
		static T& instance();
		
		/// Destruct the sole instance of type \a T.
		///
		static void destruct_instance();
	
	private:
		
		static scoped_ptr<T> _instance;
};

////////////////////////////////////////////////////////////////////////////////
// Convenience Macro's                                                        //
////////////////////////////////////////////////////////////////////////////////

/// Get the sole instance of type \a T.
///
#define the(T) \
	Singleton<T>::instance()

/// Destruct the sole instance of type \a T.
///
#define destruct_the(T) \
	Singleton<T>::destruct_instance()

////////////////////////////////////////////////////////////////////////////////
// Function Implementations                                                   //
////////////////////////////////////////////////////////////////////////////////

template <class T>
T& Singleton<T>::instance() {
	if (!Singleton<T>::_instance)
		Singleton<T>::_instance.reset(new T);
	return *Singleton<T>::_instance;
}

template <class T>
void Singleton<T>::destruct_instance() {
	Singleton<T>::_instance.reset();
}

template <class T>
scoped_ptr<T> Singleton<T>::_instance;

#endif // SINGLETON_HPP
